1. Field of the Invention
The present invention relates to a generator of a digital or analog signal with an adjustable waveform.
2. Discussion of the Related Art
For certain applications, it is desirable to have a generator of a digital or analog signal with a waveform that is adjustable according to needs. Such a generator may be used to provide synchronization pulses included in an analog video signal and which are especially used to control the passing from the end of the display of an image line to the beginning of the display of the next line and the passing from the end of the display of an image to the beginning of the display of the next image. Such a generator may also be used to provide specific digital messages intended to be inserted in a digital data flow, such as for example end of active video or start of active video signals EAV or SAV. Such messages are for example present in a digital video data flow defined according to standard ITUR-656.
A first conventional example of a digital signal generator provides a memory in which are stored all the signal values. The signal is then obtained by successively reading the values stored in the memory. To obtain an analog signal, it is then enough to convert the obtained digital signal via a digital-to-analog converter. If the memory is a RAM (random access memory), such a signal generator may provide signals of any form by modifying the values stored in the memory. Such a signal generator is generally used to provide signals of very simple form, for example, periodic signals of short period and is conventionally used for the provision of a sinusoidal signal. However, as soon as the signal to be provided is relatively complex, the number of values to be stored in the memory becomes very high, requiring use of a RAM of large dimensions and of high cost.
A second conventional example of a digital signal generator implements a state machine, for example formed by a dedicated circuit, each state corresponding to the provision of a value of the desired signal. By making the transitions between states dependent on parameters which can be modified, it is possible to change the waveform of the obtained signal. Such a state machine is, for example, used for the provision of analog video signal synchronization pulses which have different waveforms according to video signal standards. However, the flexibility of a state machine is limited since all the states and all the transitions between states likely to be of interest must have been provided before forming of the state machine. For example, the parameters enabling modifying the transitions between states may be determined to enable provision of different types of synchronization pulses according to existing standards. However, a new standard may take the lead, which requires synchronization pulses of different shape that cannot be obtained with the same state machine. Further, a state machine generally corresponds to a complex dedicated circuit, the design of which is difficult and the proper operation of which cannot easily be exhaustively verified.